1. Field of the Invention
The present invention relates to a so-called front-opening interface mechanical standard (FIMS) system used when wafers held in a transfer container which is called a pod are transferred among semiconductor processing apparatuses in a semiconductor manufacture process or the like. To be more specific, the present invention relates to a FIMS system which has a purging mechanism for cleaning an inside of the pod and in which the pod serving as an airtight container for containing the wafers, which is called a front-opening unified pod (FOUP), is placed and the wafers are moved with respect to the pod by opening/closing a lid of the pod, i.e., a lid opening/closing system.
2. Description of the Related Art
Up to now, a semiconductor manufacture process has been conducted in a so-called clean room in which semiconductor wafers are treated with high cleanliness maintained therein. However, in order to cope with an increase in wafer size and reduce a cost required for maintenance of the clean room, a method of maintaining only the inside of a processing apparatus, the pod (wafer container), and a mini-environment for substrate transfer from the pod to the processing apparatus in a highly clean state is employed in recent years.
The pod includes a main body portion having a substantially cube shape and a lid. The main body portion includes a rack capable of holding a plurality of wafers therein in a state where the wafers are separated from one another in parallel and an opening which is provided on a surface of the main body and is used for putting in/taking out wafers. The opening is closed with the lid. A pod in which a forming surface of the opening is located not vertically below the pod but on a side surface of the pod (in front of the mini-environment) is generically called a front-opening unified pod (FOUP). The present invention is mainly intended for a structure using the FOUP.
The above-mentioned mini-environment includes a first opening portion opposed to the opening of the pod, a door for closing the first opening portion, a second opening portion provided on a semiconductor processing apparatus side, and a transfer robot that moves through the first opening portion to the inside of the pod to hold the wafer and passes through the second opening portion to transfer the wafer to the semiconductor processing apparatus side. A structure for forming the mini-environment includes a mount base for supporting the pod so that the opening of the pod is simultaneously opposed to the front surface of the door.
A positioning pin inserted into a positioning hole provided on a lower surface of the pod to regulate a mount position of the pod and a clamp unit engaged with a portion to be clamped which is provided on the lower surface of the pod to fix the pod onto the mount base are located on an upper surface of the mount base. The mount base is normally movable back and forth with respect to a door direction by a predetermined distance. When the wafers in the pod are to be transferred to the processing apparatus, the pod is moved in a state where the pod is mounted until the lid of the pod comes in contact with the door. After that contact, the lid is removed from the opening portion of the pod by the door. With the operations described above, the inside of the pod is connected to the inside of the processing apparatus through the mini-environment. Subsequently, wafer transfer operation is repeated. A system including the mount base, the door, the opening portion, a door opening/closing mechanism, a wall which is a part of the mini-environment including the opening portion, and the like is generally called a front-opening interface mechanical standard (FIMS) system.
In ordinary cases, the inside of the pod with a wafer or the like loaded therein is filled with dry nitrogen or the like which is controlled to be highly clean to prevent the entry of contaminants, oxidizing gas, and the like into the pod. However, when a wafer in the pod is introduced into various kinds of processing apparatus to be subjected to predetermined processing, the inside of the pod and the inside of the processing apparatus are always kept communicating with each other. A fan and a filter are located above a chamber where the transfer robot is located such that clean air with managed particles and the like is introduced into the chamber. However, when such the air enters the pod, there is a fear that the surface of the wafer may be oxidized by oxygen or moisture in the air.
As semiconductor devices get smaller and achieve higher performance, more attention is being paid to oxidation due to oxygen and the like that enter the pod, which has conventionally not been such a big problem. Such oxidizing gas forms a very thin oxide film on the surface of the wafer or on various kinds of layers formed on the wafer. There is a possibility that, due to such the oxide film, desired characteristics of the minute devices can not be secured. Measures against this include control of the entry of gas without the partial pressure of oxygen and the like therein being controlled from the outside of the pod into the pod. To be more specific, Japanese Patent Application Laid-Open No. 11-145245 discloses a structure in which a region in a FIMS system adjacent to a pod opening is provided with a supply nozzle and a suction nozzle for gas to form an airflow curtain for substantially closing the pod opening portion. By forming the airflow curtain, the entry of external gas into the pod is prevented.
In semiconductor manufacturing equipment, there are some cases where a process using gas which contaminates various kinds of wiring and the like formed on the wafer such as an etching process is conducted in processing apparatus. A method of controlling the entry of the gas from the inside of the processing apparatus into the pod in this case is disclosed in Japanese Patent Application Laid-Open No. 2003-007799. This method also forms an airflow curtain in front of a pod opening in a FIMS system using a fan to prevent the entry of the gas from the processing apparatus into the pod. This method is considered to be effective also in controlling inflow of oxygen into the pod as a matter of course.
However, when those methods were put to practical use, it was actually confirmed that, immediately after the pod opening was opened, the partial pressure of oxygen in the pod remarkably increased. Therefore, in order to meet the above-mentioned requirement, it is necessary to further improve those methods. In light of these circumstances, the inventors of the present invention have proposed a structure of preventing oxidizing gas from infiltrating into the pod by modifying the shape and the like of a gas discharge nozzle that is used to create an airflow curtain in various ways so that the oxygen concentration in the airflow curtain is reduced in a place apart from the nozzle as well. The inventors of the present invention have also proposed a structure in which the oxidizing gas in the pod is reduced even more by introducing purge gas into the pod while forming an airflow curtain. However, further lowering of the partial pressure of oxidizing gas in a pod fixed to a FIMS system is needed because of various demands for higher semiconductor performance and improved processing ability of a semiconductor manufacturing apparatus.